Zinc smelting



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G. F. HALFACRE 2,349,619

ZINC SMELTING ATTORNEYS May 23, l944 G. F. HALFACRE ZINC SMELTING 1941 2 Sheets-Sheet 2 Filed Nov. 21

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INVENTOR @gorge E Haz/fa cre BY www ATTORNEYS ZINC SMELTING George F. Halfaore, Palmerton, Pa., assignor to The New Jersey Zinc Company, New York, N. Y., a corporation of New Jersey Application November 21, 1941, Serial No. 419,897

(Cl. 26S-20) 11 Claims.

This invention is concerned with vertical retorts for zinc smelting. 'I'he invention provides an improved structure which greatly increases the useful life of the retort and may also increase its capacity and efliciency.

In zinc smelting employing a vertical retort, (see, for example, U. S. Patents No. 1,680,726, granted August 14, 1928No. 1,811,910, granted June 30, 1931, No. 1,832,354, granted November 17, 1931, and No. 1,914,482 granted June 20, 1933) a briquetted charge of carbonaceous andzinciferous materialis heated as it passes down through a high upright chamber having long side walls and short ends of refractory heat conductive material. The charge is heated by conduction through the side walls of the retort, which adjoin heating chambers through which hot gases of combustion are passed. During operation the retort is kept full of briquettes, which are withdrawn continuously from-the bottom of the co1- umn oi charge and replaced by fresh briquettes introduced in batches at the top.

The zinciferous material may comprise zinc material, such as franklinite or willemite; oxidized material derived by roasting sphalerite concentrates; refuse zinc oxide or the like. It is mixed with carbonaceous material, for example coal, and a binder, for example waste sulflte liquor, The resulting mixture is formed into briquettes which are coked in order to give them mechanical strength and the hot coked charge of briquettes is fed in batches into the top of the retort. In the retort, the zinciferous material reacts with the carbon to produce zinc vapor which is evolved at the top of the retort. As indicated above, the brlquettes from which the zinc has extracted are removed from the base of the retort continuously, and are replaced by fresh briquettes introduced in batches at the top. 4 The retort is thus kept substantially full of briquettes, whichform a loosely packed column 30' or 40' high.

The walls of the retort preferably are constructed of silicon carbide bricks. These bricks have relatively high heat conductivity and are resistant to attack by the hot charge in the retort. Nevertheless, the silicon carbide walls are .fr corroded or eroded. Thus, the wall eventually becomes so thin that the retort must be torn down and rebuilt. With some charges, the attack upon the retort wall is localized. Thus, with a charge containing franklinite, maximum attack occurs upon the upper third or quarter of the long side walls and upon the lower third or quarter of the short end walls.

- where attack tends to be greatest, thus providing I have discovered that attack upon the walls is greatly reduced by providing a series of short pegs one above another (i. e. extending upwardly) on the interior of the retort wall, especially at the points where attack tends to be most serious.

Conveniently, the pegs are formed by bricks set in sockets ln the wall so as to project slightly, say, 1" to 2", from the otherwise smooth interior retort surface. The pegs should not be so long that they interfere seriously with the passage of charge down through the retort or tend to cause the charge to bridge. However, in a retort that is approximately 10" or 12" wide (measured from long side wall to long side wall) both side walls may be provided with pegs that project about 11/2 into the retort.

The pegs bring about a great increase in the life of the retort wall, although the reasons for the increased life (which may be or more in some cases) are not thoroughly understood. It may be that the pegs act as heat radiating uns and thus aid conduction of heat through the wall of the retort to the charge. On the other hand. the pegs may serve to hold a thin layer of depleted and hence unreactive charge against the walls of the retort and thus offer them protection.

Preferably the pegs are staggered and comprise offset bricks set in echelon in the walls. The pegs on one wall should not match the pegs on the opposing wall in order to decrease restriction of flow of material through the retort.

As indicated above the retort walls are made of refractory of relatively high heat conductivity, but the Dess need not be. Thus, the pegs may be of silicon carbide, the preferred material for the walls, or they may be made of other refractory which is much less heat-conductive, for example magnesite, chromite, mulllte, fosterite, zircite, or alumina, However, if the pegs are made of refractory that expands upon heating at a diiferent rate than the material of the walls, care should be taken to construct the sockets large enough to .provide adequate expansion joints around the pegs and so avoid inducing unnecessary strains in the heated retort walls.

In my preferred structure, the pegs serve as brackets to hold a lining of refractory plaster or tile on te inside of the retort waus 1n the zones additional protection. The plaster may be of any suitable refractory, for example silicon carbide, magnesite, or chromite refractory plaster. These and other features of my invention will be more thoroughly understood in the light of the following detailed description, taken in con- Vjunction with the accompanying drawings in which:

Fig. l is an elevation, partly in section, of a vertical retort provided, in accordance with my invention, with pegs on the upper portion oi the long side walls and on the lower portion of the short end walls, where attack tends to be mpst serious with charges containing franklinite;

Fig. 2 is an elevation of the upper portion oi the right hand side wall of the retort of Fig. 1;

Fig. 3 is an elevation of the upper portion of the left hand end wall of the retort of Fig. 1;

Fig. 4 is an elevation of the lower portion of the retort of Fig. l looking at the long side wall of the retort;

Fig. 5 is a horizontal section through the retort of Fig. l taken along the line 5 8 of Fig. 2;

Fig. 6 is a horizontal section through the retort of Fig. 1 taken along the section line 6-6 of this ligure;

Fig. 'I is another horizontal section through the retort of Fig. i taken along the line 1--1 oi' these gures; l

Fig. 8 is an elevation, partly in section, of the upper portion of a modiiled t of retort structure of my invention in which the two side walls of the retort are spaced farther apart in the zone provided with pegs, so that the inside oi the plaster lining conforms to the unlined walls oi the retort below the lined portion;

Fig. 9 is a fragmentary horizontal section showing the use of bent bricks" to bow in the side walls oi the retorts when it is desired to construct a retort having dierent widths at dit ferent elevatins therein as in the case of the retort of and Fig. 1l) is a traen horizontal section showing the use of bent bricks to how out the side walls oi the retort for the 1-1- w-ef as that described in connection with Fig. 9.

Referring now to Figs. i to '2, inclusive, the retort comprises a refractory column of rectangular plan having long side walls and short end walls. The side walls are about lo" or 12" apart and the end walls are much fer apart. say, 4' to 6'. All oi the walls are de ci silicon carbide bricks. e side walls are constructed about e thick. The ends walls are much thicr and the side walls end into vertical slit joints in the end walls as described and claimed in U. S. Patent No. 1,918,245 granted July lo, 1933. The slip joints comprise vertical slots that extend from top to bottom of the retort. The ends of the side walls fit loosely in these slots. On each side of each slot there is a vertical gland which exteds the full height of the slot and which is filled with granular refractory material such as silicon carbide sand. The slip joints are required because o the difference in the expansion of side and end walls upon heating, and per mit relative movement of side and end walls with out substantial leakage.

Except at top and bottom, where the side walls are corbelled away from each other to give in creased interior cross section, the side walls are parallel to each other (as are the end walls) and the interior surface ci the walls, except for certain pegs to be described hereinafter, is smooth.

The retort adjoins heating chambers that extend irom top to bottom of the retort and are dened by refractory walls (see Figs. 1 and 8).

It has been found that with briquetted charges composed principally of carbonaceous material and franklinite concentrates, attack upon the retort is most severe on the upper third or quarter of the side walls and on the lower third or 5 quarter of the end walls. Thus the silicon carbide walls in these zones may be eaten away to a depth of 2" or 3" in a period 'somewhat less than a year. It is sometimes possible to patch the side walls by means of refractory plaster or the like held against the outside of the walls in the heating chamber, but when the walls have been reduced to a thickness of 2" or less by the attack of the charge, it is usually necessary to shut down and re-build the retort. 'I'he retorts are large and expensive, so that an improvement in structure which brings about substantial increase in the active life of the retort wall affords large savings. The pegs of my invention are such an improvement.

Referring particularly to Fig. 1, it will be observed that the pegs are formed by refractory bricks which are oiset from the other bricks of the retort wall so that they project into the retort a short distance, say, 11/2". Thus (as shown in Figs. 2 and 3), in every sixth course two bricks of the eight (or about every third brick) in the upper portion of the end walls are oiset so that they extend into the retort space. The onset bricks are of the same size and shape as the standard bricks which form the bulk of the side walls and are backed by .so-called soap bricks which are slightly more than half as thick as the standard brick. In consequence, the soap bricks project slightly on the outside of the retort wall.

As indicated above, the bricks which form the pegs inside the retort may be of the same material as the bulk of the wall, say, silicon carbide, or they may be of other and less heat-conductive refractory, say, chromite or magnesite. In any case, however, it is desirable that the soap" bricks which back the offset bricks be of the saine material as the brick of the retort wall, so that there may be a continuous column of a-re fractcry with the same co-emcient of expension et from top to bottom of the retort. Otherwise, severe strains are likely to be induced in the retort structure due to the interposition in the column of bricks with a different coefllcient ot expension than the bulk of the retort wall.

Now considering the upper portion of the retort in greater detail, attention is directed to Figs. 2 and 3 which show that the offset bricks (pegs) in the side walls are set in staggered rows ive courses apart, the. arrangement being such that the offset bricks in the left hand wall (Fig. 2) are not directly opposite the oiset bricks in the right hand wall (Fig. l). In this manner, the protection is afforded to the Walls by the pegs, but with minimum constriction of the retort space with consequent reduction in the tendency of the briquettes to bridge and hang up in the column.

It has been found that the pegs alone bring about an increase in retort life, but this benelcial effect can be enhanced by employing the pegs as brackets to support a refractory plaster or tile lining. A plaster lining, approximately 1" thick, and applied in two 1/2" layers, is provided in the upper portion of the retort of Figs. 1 to 7 on both side walls. It will be observed that the pegs project slightly, say, about 1/2" through the plaster. This is desirable, for the pegs projecting through the plaster have the effect of reducing the attack thereon in addition to holding it in place and preventing it from sliding down the retort wall after the retort has been heated' and the plaster has shrunk. A plaster consisting largely of line silicon carbide or chromite with a small proportion of iine clay binder is satisfactory.

Thin tiles (not shown) may be substituted for the plaster lining if desired, the tiles being of'such size and arranged in such a pattern that they are adequately supported by the offset bricks (pegs) To consider the pegs in the lower third or quarter of the end walls, reference should be made to Figs. 4 and '7. As shown in these figures there is an oiset brick or peg in the end walls about every tenth or eleventh course. These bricks, like those in the side walls, are offset about 1" to 1%" and serve to support a refractory plaster lining of the same character and thickness as that on the end walls. Because of the greater distance between end walls (as compared with that between side walls) it is unnecessary to stagger the pegs so the offset bricks may b e placed opposite each other, if desired.

It should be understood that the pegs may be employed at zones other than those so shown in Figs. i to '7, inclusive, and in fact my be employed advantageously on the entire interior of the retort wall. v

As disclosed hereinbefore, it is desirable to provide projections on the outside of the retort side walls which match the pegs on the inside walls. Such outside matching projections are conveniently formed of narrow silicon carbide bricks (soaps) which back the pegs projecting into the retort. The outside projections may be employed as supports for patches which serve to prolong the useful life of the retort when the side walls, despite the protection afforded by the interior pegs with or without plaster, have been eaten away to a substantial degree. Thus, plaster or thin tiles may be applied to the outside of the retort side walls in much the same manner as that described for the inside walls.

Refractory braces may be employed to hold the patches in place on the Voutside of the retort walls. Thus bricks may be wedged between the patch and the outer wall of the retort. Figs. l and 8 illustrate the application of tile or plaster patches to the outside of the retort side wall when this wail has become very thin. The projections provided by the soap bricks support the plaster or tile, lateral movement being prevented by braces such as refractory bricks wedged between the retort wall and the outer wall of the heating chamber.

Fig. 8 illustrates a modified type of retort structure which may be employed advantageously when the two side walls of the retort areclo'se,

- together (say with argap of about 10" or less) in the lower portion of the retort. As shown in Fig. 8, the lined wall sections in the upper third or quarter of the retort are corbelled out slightly from the lower wall portions, so that they may i be lined with plaster the surface of which is and continuous, without oisets, so that the side walls may move vertically and as units with respect to the end walls.

As indicated above, the 'plaster employed on retort walls may be of any suitable refractory. A suitable chrome plaster is made by mixing about 100 lbs. of finely divided 'conventional chrome refractory with 4 lbs. of fire clay and 3 lbs. of waste sulilte liquor plus water to trowel. Silicon carbide plaster should contain at least 70% of silicon carbide and preferably in excess of the balance being composed of fire clay and sulfite liquor and water as in the case of the chromite plaster.

I claim:

l. In a vertical retort adapted for reducing a charge of mixed carbonaceous and zinciferous material comprising an upright chamber filled with the charge and walled with a heat conductive refractory, the combination which comprises an upwardly extending series of short pegs of refractory material on the inside of the wall of `the chamber, and a relatively thin refractory lining covering the inside of the wall and supported by I the pegs, and means for heating the charge by conduction through said wailvfrom the outside thereof.

2. In a vertical retort adapted for reducing a charge of mixed carbonaceous and zinciferous material comprising an upright chamber walled with a heat conductive refractory, the improvement which comprises an upwardly extending series of staggered short pegs of refractory material on the inside of the wall of the chamber, and matching shallow projections of refractory material on the outside of the wall of the chamber.

3. In a vertical retort adapted for reducing a charge of mixed carbonaceous and zinciferous material comprising an upright chamber having walls of refractory heat conductive bricks, the improvement which comprises an upwardly extending series of short refractory pegs set in sockets on the inside of the walls and formed of refractory bricks that are diiferent in composition from the bulk of the wall, the projecting bricks being backed by bricks of the same material as that employed in the bulk of the walls.

4. In a vertical retort" adapted for reducing a charge of mixed carbonaceous and zinciferous material comprising an upright chamber walled with a heat conductive refractory, the improvement which comprises an upwardly extending series of short pegs of refractory material on the inside of the wall of the chamber, and a relatively thin lining of refractory material disposed on the inside of the wall and supported by the pegs, with the pegs extending through the lining.

5. In a vertical retort adapted for reducing a charge of ymixed carbonaceous and zinciferous material comprising an upright chamber filled with the charge and walled with a heat conductive refractory, the combination which comprises an upwardly extending series of short pegs of refractory material on the inside of the wall of the chamber, the pegs being discontinuous around any horizontal section of the chamber, and means for heating the charge by conduction through said wall from the outside thereof.

6. In a vertical retort adapted for reducing a charge of mixed carbonaceous and zinciferous material comprising an upright chamber filled with the charge and having long side walls and short ends of refractory heat conductive bricks, the combination which comprises an upwardly extending series of short refractory pegs on the inside of the side walls adjacent the top of the chamber. the pegsfbeing so arranged as to be discontinuous along any horizontal section of `said side walls, and means for heating the charge by conduction through ,the side 'walls from the outside thereof.

7. In a vertical retort adapted for reducing a charge of mixed carbonaceous and znciferous material comprising an upright chamber filled with the charge and having long side wallsand short ends of refractory heat conductive bricks, the combination which comprises an upwardly extending series of short refractory 'pegs on the inside of the end Walls near the bottom of the chamber and discontinuous around any horizontal section in the retort, and .means for heating the charge by conduction through said walls from the outside thereof.

8. In a vertical retort adapted for reducing a charge of mixed carbonaceous and zinciferous material comprising an upright chamber filled with the charge and walled with heat conductive refractory bricks, th combination which comprises an upwardly extending seriesoi' short pegs formed by offset refractory bricks disposed on the inside wall of the chamber but discontinuous around any horizontal section of the chamber, and means for heating the charge by conduction through said wall from the outside thereof.

9. In a vertical retort adapted for reducing a charge of mixed carbonaceous and.zinciferous material comprising an upright chamber iilled with the charge and having walls of refractory heat conductive bricks, thecombination which comprises an upwardly extending series of staggered short refractory pegs on the inside of the wail of the chamber, the pegs being so arranged as to be discontinuous around any .horizontal sectionl of said wall, and means for heating the charge by conduction through said wall from the outside thereof.

10. In a vertical retort adapted for reducing a charge of mixed carbonaceous and zinciierous material comprising an upright chamber illied with the charge and having walls of refractory heat conductive bricks, the combination which comprises an upwardly extending series of short refractory pegs on the inside of the wall of the chamber and formed of oifset refractory bricks set in sockets in the wall and discontinuous around 'any horizontal section of the chamber, and .means for heating the charge by conduction through said wall from the outside thereof.

11. In a vertical retort adapted for reducing a charge of mixed carbonaceous and zinciterous material comprising an upright chamber filled with the charge and having long side walls-and short ends of refractory heat conductive bricks,

g5 the combination which comprises an upwardly 80 the pegs on the opposite wail, and means for heat ing the charge by conduction through said wail from the outside thereof.

GEORGE F. HALFACRE. 

